My mom usually puts a yule log on my brother and grandparents graves. It is a planter type box made out of a log and filled with greens and usually a few silk flowers. They sell them at a lot of the nurseries and farmers markets around here. Another popular item in that cemetary is the evergreen wreaths on the stands. They don't have headstones there (just plaques in the ground) so there is nothing to attach a wreath too. They also turn down the vases for the winter, so you can't use them.
She has also bought holiday yard stakes in the past (not just for xmas but for other holidays too). She also has one of those mini garden flag things at my brothers grave and she changes the flag seasonally. She has only lost one flag so far, but she thinks the wind blew it off (but it might have been stolen for all she knows)......